Jet nozzle

ABSTRACT

The disclosure of this invention pertains to a jet nozzle for a gas turbine engine wherein the throat diameter of the nozzle is defined by the downstream end of an annular arrangement of flaps connected to a jet pipe and pivoted by a shroud surrounding the flaps being moved axially along the jet pipe. Between the shroud and each of the flaps there is provided a cam and roller device to convert the movement of the shroud into that of the flaps. The shroud comprises walls extending at a boat tail angle and in relatively close proximity to the flaps, from the position of maximum throat diameter to a larger diameter upstream thereof, each wall extending between two adjacent said cam and roller devices, and each of these devices is housed by a strake connected to the adjacent walls. The arrangement of the walls and the strakes ensures low-base drag.

United States Patent McMurtry [451 Feb. 22, 1972 [54] JET NOZZLE 3,403,858 10/1968 Kurti et al ..239/265.39 [72] Inventor: David Roberts McMurtry Bristol, England 3,060,681 10/1962 Morley eta1.. ..239/265.37 X [73] Assignee: Rolls-Royce Limited, Derby, England Primary Examiner-Lloyd L. King Assistant ExaminerReinhold W. Thieme [22] lune 1970 AttorneyMawhinney and Mawhinney [21] App1.No.: 45,526

[57] ABSTRACT [30] Foreign Application Priority Data The disclosure of this invention pertains to a jet nozzle for a gas turbine engine wherein the throat diameter of the nozzle is Sept. 6, 1969 Great Britain ..30,997/69 defined by the downstream and of an annular arrangement of flaps connected to a jet pipe and pivoted by a shroud surrounding the flaps being moved axially along the jet pipe. 58] E d 39 265 43 Between the shroud and each of the flaps there is provided a o are cam and roller device to convert the movement of the shroud into that of the flaps. The shroud comprises walls extending at [56] Reierenoes cued a boat tail angle and in relatively close proximity to the flaps, UNITED STATES PATENTS from the position of maximum throat diameter to a larger diameter upstream thereof, each wall extending between two Dl'elfke X adjacent said cam and roller devices and each of these 3,024,599 3/1962 Keen ..239/265.37 devices is housed by a Snake connected to the adjacent walk 2,927,424 3/1960 y The arrangement of the walls and the strakes ensures low-base 2,806,349 9/1957 Yeager ..239/265.39 X drag 1 2,926,489 3/1960 Halford et al.. 239/265.39 2,976,676 3/ 1961 Kress ..239/265.39 UX 4 Claims, 7 Drawing Figures IIIIIIIIIIIIIIII" JET NOZZLE This invention relates to a jet nozzle for gas turbine engines.

In a known form of nozzle the flow area or throat of the nozzle is varied by an annular arrangement of flaps whose downstream ends lie in an annulus defining said throat and which are pivoted at their upstream ends to a jet pipe, and in respect of each flap there is provided a mechanism connecting the flaps to a shroud surrounding the flaps such that if the shroud is moved axially the flaps are pivoted to vary the diameter of said throat.

The presence of the mechanism makes it necessary for the shroud to have a significant radial thickness, and this is a source of base drag on the aircraft in respect of which the engine is installed.

Normally, base drag in an aerodynamic structure is avoided by tapering the downstream end of the structure to an appropriately small so-called boat tail angle.

In the case of a nozzle as described above, this would means that if undue base-drag is to be avoided said shroud has to be extended a substantial distance downstream of the throat. This not only imposes a weight and size penalty on the engine but is also undesirable in that it may inhibit the free expansion of the According to this invention there is provided a jet nozzle for a gas turbine engine wherein the minimum flow area or throat of the nozzle is varied by an annular arrangement of flaps whose downstream ends lie in an annulus defining said throat and which are pivoted at their upstream ends to a jet pipe, and wherein there is provided in respect of each flap a mechanism connecting the flaps to a shroud surrounding the flaps such that if the shroud is moved axially the flaps are pivoted to vary the diameter of said throat, characterized in that the shroud comprises a conical arrangement of walls extending at a boat tail angle from the position of maximum throat diameter to a larger diameter upstream thereof, each of the walls extending between two adjacent said mechanisms, and wherein there is provided in respect of each mechanism a strake connected to the adjacent walls and extending radially outwards therefrom to enclose the mechanism.

The arrangement of said walls and strakes makes it possible for flight wind over the shroud to converge gradually to the maximum throat diameter and so make it possible to reduce base drag without the need to extend the shroud significantly downstream of the ends of the flaps.

Said walls may be adapted to be extensible in the downstream direction for the purpose of compensating at least partially for an increase in base drag when the shroud is moved to pivot the flaps radially inwards from the position of maximum throat area.

An example of a nozzle according to this invention will now be described with reference to the accompanying drawings wherein:

FIG. 1 is a side elevation of the nozzle.

FIG. 2 is a fragmentary plan view of FIG. 1.

FIG. 3 is an end view of FIG. 1.

FIG. 4 is a section on the line lVlV in FIG. 3.

FIG. 5 shows FIG. 4 in a different operational position.

FIG. 5a is a section on the line Va-Va in FIG. 4.

FIG. 6 is a section on the line VI-VI in FIG. 3 and embodies a modification.

FIG. 7 shows FIG. 6 in a different operational position.

Referring to FIGS. 1 to 5, a jet engine 10 has a jet pipe 11 terminating in a nozzle 12 situated downstream of a cowl or nacelle 13 enclosing the engine. The nozzle includes an annular arrangement of flaps 14 whose downstream ends lie in an annulus defining the minimum flow area or throat, denoted 16, of the nozzle. To enable the throat diameter to be varied each flap is connected at its upstream end to the jet pipe by pivots 15. FIGS. 4 and 5 show the maximum and minimum throat positions of the flaps denoted 14A and 14B respectively.

Each flap is adapted to be pivoted by a mechanism 20 operated by a shroud 21 surrounding the nozzle and supported 2 l l on the jet pipe for movement therealong under the action of fluid pressure motors 22. In the present example each mechanism 20 comprises a cam 23 forming part of} the associated flap and a roller 24 supported by the shroud. FIG. 4 shows the shroud in the extended or downstream position in which the flaps form the maximum throat diameter'while FIG. 5 shows the shroud in the retracted or upstream position being the position corresponding to minimum throat diameter.

The shroud comprises an annularly continuous wall 30 surrounding the downstream end of the jet pipe with a clearance necessary, for example, to allow for'the presence of the flap pivots and of the connection between the shroud and the mo tors 22. The shroud further comprises'an arrangement of walls 31 converging from the wall 30 and terminating at their downstream ends at a position close to the downstream ends of the flaps when the latter are in the position of maximum throat area. In this way it is possible to give the shroud an aerodynamically satisfactory boat tail angle a (FIG. 1) and substantially avoid the occurrence of base drag in the maximum throat diameter position of the flaps. It will be noted that in the FIG. 5 position the walls 31 are virtually in line with the taper of the nacelle surface while in the FIG. 4 position the wall 30 defines the transition between the nacelle and the walls 31.

The walls 31 extend peripherally between the mechanisms 20, i.e., radially inwardly of the maximum radial extent thereof. To house the mechanisms there are provided elongate projections or strakes 32 projecting from between adjacent walls 31. The strakes 32 are elongate in the direction of airflow. The strakes are streamlined as particularly shown in FIG. 2 so as not to present any significant drag problem. The walls 31 are connected at their downstream ends by an annular member 33 which provides the necessary hoop strength against the loads on the rollers 24. The member 33 is polygonal, i.e., it is straight between successive rollers 24 so as to be stressed in tension only. The walls 31 are correspondingly shaped to be flat at least towards their downstream ends. The flaps 14 are shaped so as to form angles B fitting the shape of the walls 31. Gaps between adjacent flaps 14 are covered by auxiliary flaps 16 (FIGS. 1, 3).

It will be seen that in the FIG. 4 position the base drag area, denoted C, is minimal. However as soon as the flaps are pivoted inwardly base drag occurs at the outside of the flaps. To reduce this, the modification shown in FIGS. 6 and 7 provides for the walls 31 to be made extensible by being each provided with a plate 34 supported on the wall 31 by guides 35,

36 for movement towards and away frornthe apex of theconical arrangement of the walls. Each plate 34 is connected to the jet pipe by a link 37 which controls the position of the plate so that when the shroud is in the FIG. 6 position the downstream ends of the wall 31 and the plate 34 coincide, but when the shroud is moved into the FIG. 7 position the plate does not participate in the upstream motion but is merely lowered from the position 34A into the position 34B. In consequence the taper of the walls 31 is extended to a position relative to the flaps in which the base drag area of the nozzle is given by the dimension D as distinct from the larger dimension E which would apply if the walls 31 are not extended.

It will be appreciated that the plates 34 may be moved independently of the walls 31 by any appropriate mechanism and not necessarily by the links 37.

What we claim is:

1. A jet nozzle for gas turbine engines wherein the minimum flow area or throat of the nozzle is varied by an annular arrangement of flaps whose downstream ends lie in an annulus defining said throat and which are pivoted at their upstream ends to a jet pipe, and wherein there is provided in respect of each flap a mechanism connecting the flaps to a shroud surrounding the flaps such that if the shroud is moved axially the flaps are pivoted to vary the diameter of said throat, characterized in that the shroud comprises a conical arrangement of walls extending at a boat tail angle from the position of maximum throat diameter to a larger diameter upstream thereof,

each of the walls extending between two adjacent said mechanisms, and wherein there is provided in respect of each mechanism an elongate housing connected between the adjacent walls and extending radially outwards therefrom to enclose the mechanism.

2. A jet nozzle according to claim 1 wherein the mechanism comprises a cam secured to the flap and a roller supported for rotation within the strake, the cam extending into the strake through a gap between the adjacent walls and cooperating to pivot the flap when the shroud is moved.

3. A jet nozzle according to claim 1 comprising in respect of 

1. A jet nozzle for gas turbine engines wherein the minimum flow area or throat of the nozzle is varied by an annular arrangement of flaps whose downstream ends lie in an annulus defining said throat and which are pivoted at their upstream ends to a jet pipe, and wherein there is provided in respect of each flap a mechanism connecting the flaps to a shroud surrounding the flaps such that if the shroud is moved axially the flaps are pivoted to vary the diameter of said throat, characterized in that the shroud comprises a conical arrangement of walls extending at a boat tail angle from the position of maximum throat diameter to a larger diameter upstream thereof, each of the walls extending between two adjacent said mechanisms, and wherein there is provided in respect of each mechanism an elongate housing connected between the adjacent walls and extending radially outwards therefrom to enclose the mechanism.
 2. A jet nozzle according to claim 1 wherein the mechanism comprises a cam secured to the flap and a roller supported for rotation within the strake, the cam extending into the strake through a gap between the adjacent walls and cooperating to pivot the flap when the shroud is moved.
 3. A jet nozzle according to claim 1 comprising in respect of each said wall a platelike member supported on the wall for sliding motion towards and away from the apex of the conical arrangement of the walls, and means for moving the members relative to the walls, thereby to vary the length of the boat tail defined by the walls.
 4. A jet nozzle according to claim 3 wherein each said member is connected to the jet pipe by a link so that said relative movement of the members is effected by the movement of the shroud. 